Removal of mud cake in casing cement jobs



Patented Aug. '10, 1943 REMOVAL OF MUD CAKE IN CA SING CEMENT JGBS JamesU. Tcague; New EDrleans, La., and George E. Cannon, Houston, Tex,assignors to Standand Qil Development Company, a corporation of DelawareNo Drawing. Original application September 27,

1939, Serial No. 296,734. Divided and this application Januar 1, 1943,Serial No. 471,022

2 (Jlaims. (o1. lose-22) The present invention-relates to the cementingof easing into a. bore hole and is a division of U. S. Ser. No. 296,734,filed September 2'7, 1939. r

In completing wells it is common to set a casing in the bore hole. Acement mixture is then pumped into casing so that it passes out of thelower end of t casing and rises in the annular space between the .ingthe lower end of the casing, the water producing formations above theoil producing formations are sealed 011 from the oil producing formation.and are prevented from producing the water along with the oil andperhaps eventually drowning the oil well. It is also quite usual for anoil formation to have a gas cap or for the oil in the formation tocontain dissolved gas and asing and the bore hole and is then allowed toset in this annular space form-1 action is such that when the cement ispumped under such conditions the cementing of the cas- I ing may preventgas from flowing up to the surface of the earth in the space between thebore hole wall and the casing, or may serve to reduce the gas-oil ratioin the oil produced.

It has been found that in many instances the cementing of the lower endof the casing produced unsatisfactory results in that a tight seal isnot established between the formation and the casing wall. Manydisadvantages arise from the failure of a cementing job. It isquiteoften necessary-to go back into the hole andrecement the casing inorder to shut off excess gas or to stop the flow of water into the hole.7

It has now been found that in many cases a poor cementing job is due tothe fact that the conventional mud filter cake formed on the walls ofthe hole during the rotary drilling operation prevents the cement fromforming a tight bond with the formation. a

It has now. been discovered that by removing the mud cake from theportion of the hole where the cement is to be deposited the cement willform a tight bond between the formation penetrated by the bore hole andthe wall of the Gasing and will form an efiective. seal in the borehole.

Several methods are available to remove a filphosphate, sodiummetasilicate, alkaline tannate solution and other likechemicals whichare used to reduce the viscosity of drilling mud. When these dispersingagents passacross the face of the filter cake they tend to soften,disperse and remove the cake. While on some occasions they may notcompletely remove the cake, yet their into the bore hole the cake is sosoft that the cement removes the cake as it flows upwardly in theannular space between the casing and the bore hole.

Another method of removing the mud cake from the portion of the borehole where the cement is to bedeposited is by increasing theabrasiveness of the cement slurry used for cementing the casing. Inother words, while it is usual in cementing jobs to use neat cement,that is a mixture of Portland cement and water, we have found that bymixing sand or other-similar materials which are harder and have alarger particle size than cement with the cement an abrasive mixture wasobtained which when pumped into the bottom of the hole and-across theface of the filter cake erodes. and removes the mud filter cake from thewall of the formation and allows the cement cake to bond directly fromthe formation to the wall of the casing.

Under some circumstances, it'may be advisable to combine the twoabove-mentioned methods. In carrying out this procedure a dispersingagent is pumped ahead of the cement and inaddition abrasive particlesare added to' the cement mixture which is pumped down after thedispersing agent. Any part of the mud cake which is not removed by thedispersing agent is readily removed by the mixture of cement andabrasive material which follows the dispersing agent.

Modifications of the above described preferred forms of the inventionwill suggest themselves to a skilledworker and it is, therefore, not our.intention to be limited to the above described procedures, but only bythe limitations expressed,

in the claims appended hereto.

We claim:

the cement particles in the slurry.

v JAMES U. TEAGUE.

GEORGE E.'CANNON.

1. In the cementing'of casing in-a bore hole :the step of using cementslurry mixed with sand.

